Of motherhood, "It really does crack you open in every way," said the actress. "I never knew that I could be so tired. I never knew that I could work so hard. I never knew that I could love so much or be so patient or be so excited by the tiniest, tiniest little thing. Everything about it has surprised me."

It took the challenge of a unique and high-profile movie The Dark Knight, in which Gyllenhaal co-stars with Christian Bale and the late Heath Ledger, to get her back to work.

In the film, she plays Rachel Dawes, Batman's love interest, taking over the role from Katie Holmes, who played the part in the previous film.

"I do think that it's really difficult to get me away from [Ramona]," she said. "It's difficult to find a script that's good enough for me to think, 'Okay, I really need to do this instead of being with my daughter.'"

Known for her edgy performances, Gyllenhaal filmed Farlanders for director Sam Mendes last spring, "but mostly I've been with her," she says. "Some people have asked me whether I'll choose things that ... have a more sort of child-appropriate content, and I don't think so. I think I'll choose what's interesting to me."

Gyllenhaal says she receives tremendous support balancing parenthood and career from fiancé, Peter Sarsgaard. "We share absolutely equally," she explained, and added that her brother Jake Gyllenhaal is "a great uncle."